The invention relates to a cooling fan with an electric motor drive, especially for use as a cooling fan in a motor vehicle.
The cooling fan is taken to mean the fan system which essentially consists of the fan wheel with fan wheel hub and fan blades and an electric motor to drive the fan. Usually this type of cooling fan is mounted for example in a frame provided for the purpose which is fixed in the engine compartment of a motor vehicle or such like.
For safe operation of electric motors it is necessary for the components and materials used not to become overheated under specific operating conditions. It is therefore necessary to ensure that no overheating occurs during the operation of the electric motor with maximum power dissipation. If this requirement is not observed the result can be a reduction in the lifetime of the electric motor or a total failure of the electric motor. The cooling of the electric motor, that is the removal of the waste heat generated by the electrical components, especially in the commutator, the coil and in the iron components to which electromagnetic forces are applied, is of major significance.
Today's electric motors are equipped with electronics for brushless commutation or speed regulation/controlling for example, which may also release large amounts of waste heat. This electronics represents the components of an electric motor which are critical from the thermal standpoint and increases the cooling requirements.
Use as a drive unit of a cooling fan for the internal combustion engine in a motor vehicle, as a result of the extreme changes in environmental conditions, such as operation during summer and winter for example also increases the requirements for managing the heat produced by the electric motor used.
With electric motors used to drive fans routing an air flow through the electric motor by generating and using a difference in pressure between air inlet openings and air outlet openings of the electric motor housing is known.
Thus for example publication EP 1 050 682 A2 shows a cooling fan with electric motor. This involves an electric motor with an internal wound stator and a permanently excited external rotor. The motor electronics is located in a chamber on the outside of what is known as the stator foot of the electric motor and is covered by a separate cover. The fan wheel hub is embodied in the form of a bowl and features air scoops on its inside which generate a cooling air flow. The cooling air flow is directed sideways past external cooling ribs of the stator foot into the interior of the electric motor housing and leaves the housing on the opposite side through openings in the floor of the dish-shaped external rotor and the air gap between the fan hub and the external rotor.
The electronics is encapsulated by enclosing it under a separate cover and the heat losses generated can only be removed by heat conductance via the stator foot. The heat conduction path from the electronics to the cooling fins of the stator foot is comparatively long in this case. The cooling air flow generated can only accept the heat energy generated by the electronics at one point over a comparatively short path past the cooling fins. The heat losses generated by the stator winding can only be removed via the cooling air flow since the air gap between stator and rotor practically operates as a heat isolator. Thus practically no heat can be removed via the external surfaces of the electric motor. These design features make effective removal of heat losses more difficult In addition the arrangement of the electronics requires an additional housing cover which encloses the mounting chamber.
A further electrical fan, especially for motor vehicles, is disclosed in Application DE 100 44 066 A1. In the electrical drive motor used here the electronic control unit used to control the fan motor is housed with this in a shared housing. A cooling air flow which can be generated by the fan wheel is also routed through ventilation openings of the housing. To cool the control unit this is equipped with at least one heat sink which is attached to the rear end plate arranged in a ventilation opening of the housing and thus cooled by the cooling air flow. This requires separate heat sinks and mounting connections between heat sinks, control unit circuit board and bearing cover of the housing. A additional heat removal on the outside of the motor housing cannot be undertaken here either in any of the embodiments since the cooling air flow only passes over the components generating the individual heat once.